1. Graduate School of Environment and Information Sciences Yokohama National University Hodogaya‐ku, Yokohama Japan
2. Graduate School of Informatics and Engineering The University of Electro‐Communications, Fuda Chofu Japan
3. Department of Applied Mathematics, Computer Science and Statistics Ghent University Ghent Belgium
4. Department of Mathematics Babeş‐Bolyai University Cluj‐Napoca Roumania